1. Field of the Disclosure
The disclosure generally relates to joint evaluation, and more particularly to a method and analysis system to determine a joint equilibrium position.
2. Description of Related Art
The knee joint is composed of the femur or thigh bone, the tibia or shin bone, and the patella or knee cap. The bones are connected by fibrous structures called ligaments, which allow a certain amount of “joint play” or motion to exist between the bone structures. When this joint play is increased or decreased, an abnormal or pathological condition exists in the knee. Attempts have been made in the past to quantify this increase or decrease in joint play of the knee with limited success.
Knee injuries often cause damage to one or more of the structures that form the knee joint. Such injuries typically cause an increase in joint play or motion of the knee. A patient may interpret an increase in joint play as a sensation that the knee is slipping or coming out of joint. In other words, this sensation may be described by the patient as the feeling of joint instability. Knee instability may be related in part to an increase in the length of the ligaments that connect the bones together, an increase or change in compliance (elastic resilience or stretchiness) of the ligaments, or both. Knee instability may also be related in part to the shape and size of the joint bones. The degree or likelihood of the knee joint bones actually coming out of joint or becoming unstable is related to the amount of stretch or increased length of each knee ligament, the number of knee ligaments involved, and the existence of damage to one or more other support structures of the knee joint, such as the joint bones themselves, the menisci, or the like. Accurate measurement of an increase in ligament length can be critical to restoring a patient's injured or damaged knee to as close as possible to its original functional and anatomical structure and condition.
For the most part, knee injuries and ligament damage have been diagnosed using only manual tests. These tests are performed by doctors or other medical personnel, i.e., clinicians, on the patient in order to detect and measure joint play to diagnose damage to the knee ligaments or other knee joint support structures. There are a number of commonly known manual tests used to evaluate increased joint play that is usually associated with an anterior cruciate ligament (ACL) tear. These tests include the Lachman test, the Pivot Shift test, and the Anterior Drawer Test. Additional manual tests are known for evaluating other ligament injuries in the knee. These tests include the dial test and the Varus-valgus test. Because all of these tests are performed manually by individual medical personnel, these tests naturally are limited by the specific clinician's subjective evaluation. The subjective nature of the tests may hinder the precision or accuracy of any diagnosis of the extent of ligament lengthening, the change in ligament compliance or elastic resilience, i.e., stretchiness, or combinations thereof.
The Lachman test is performed with a patient lying in a supine position. The clinician will bend the patient's knee joint at approximately 20 to 30 degrees. The clinician places one hand on the patient's upper thigh and their other hand below the upper part of the patient's calf. The clinician then applies upward pressure under the patient's calf and downward pressure on the patient's thigh. The clinician further applies downward pressure on the patient's lower leg and upward pressure on the patient's thigh. These maneuvers induce anterior-posterior translation between the patient's femur and tibia. The degree of translation is subjectively determined by the clinician to diagnose the injury or joint damage.
The dial test, or the 30 degree tibial axial rotation test, is performed with the patient lying in the supine position with the knee flexed at 30 degrees and the heel on the table. The foot is rotated in maximum internal rotation followed by maximum external rotation. The amount of rotation occurring both at the proximal tibia and at the foot is noted.
The Varus-valgus stress test can be performed under many conditions, the most common one having the patient supine and the lower leg cradled in the clinician's arms. Pressure is applied in an abduction and adduction movement at the foot while a hand stabilizes the femur. An assessment of both motion and separation of the joint space is noted along its medial and lateral joint line.
The Anterior Drawer test is also performed with the patient lying in a supine position, but with the knee joint bent to about 90 degrees (x-axis rotation). The patient's foot is supported by a table or chair while the clinician applies hand pressure to the knee joint. The Anterior Drawer test is subjectively graded by the clinician based on the perceived amount or extent of anterior translation of the tibia with respect to the femur.
The Pivot Shift test may be considered to combine some or all of the foregoing tests into a complex maneuver. The Pivot Shift test is similarly performed with the patient lying in a supine position. The leg is straightened out so that the knee joint is placed in full extension (x-axis rotation). A valgus or side-to-side outward rotation (y-axis rotation) force and an internal or twisting rotation (z-axis rotation) force is applied to the knee to allow the lateral tibia to slip anteriorly from underneath the lateral femoral condyle. As the knee is flexed or bent (x-rotation), the tibia is allowed to slip suddenly back underneath the femoral condyle. The clinician subjectively determines whether there is an abnormal external rotation (z-axis rotation) and posterior translation (y-axis translation) of the tibia with respect to the femur. The degree of shift that is felt or determined by the clinician represents to the clinician the relative increased translation (y-axis translation) of the lateral side of the knee with respect to the increased translation (y-axis translation) of the medial side of the knee. A sudden shift in the knee joint is felt by the clinician and represents the point at which the tibia bone slides from in front of the radius of curvature of the curved end of the femur back to its normal position under the femoral condyle. The Pivot Shift test is inherently subjective, difficult to accurately perform, difficult to teach, and ultimately difficult to quantify.
Grading each test usually involves the opinion of the physician placing the test into one of three categories, such as Grade I, Grade II, or Grade III. For the Pivot Shift test, the grading depends upon the speed and intensity of the knee joint slipping back into place. For other tests, the grading represents the amount of motion detected by the clinician during the examination. For example, Grade I may be used to represent 0-5 mm of joint play. Grade II may be used to represent 6-10 mm of joint play. Grade III may be used to represent 11-15 mm of joint play. The clinician then subjectively rates the pivot shift as Grade I, Grade II, or Grade III depending upon the degree of rotational and translational shift felt during the test.
For a ligament injury to be diagnosed, the result of one or more of these tests is considered abnormal, suggesting a Grade II or more increase in joint play. In the past, the results of a single test were used to diagnose a ligament tear. Often this “one dimensional” diagnosis would result in a surgical procedure. For instance, in order for a clinician to diagnose an injured ACL using the aforementioned manual tests, the clinician determines whether the knee feels abnormal. The accuracy of an ACL injury diagnosis provided by a clinician using currently known manual tests depends on the skill and experience of the clinician and their subjective determinations. A misdiagnosis can lead to unnecessary treatment or unnecessary delay in treatment, which may result in an increased risk for further injury or damage to the patient's knee joint.
Combinations of these clinical examination tests can be used to diagnose lateral collateral ligament (LCL), medial collateral ligament (MCL), posterior cruciate ligament (PCL), and other knee ligament injuries. Each manual test relies on grading the degree of length (or damage) increase in the ligament based on relative increase in joint play into three Grades or categories. There is no effort to grade the compliance or elastic resilience, i.e., stretchiness, of the ligaments using these manual tests. An expert clinician may instead describe the ligament in terms of its subjective feel to the clinician, such as by determining that the joint has a hard or soft endpoint. Also, a knee joint may have injury or damage to more than one ligament or structure. The more ligaments and structures of the knee joint that are damaged, the more complex it is for the clinician to perform a manual knee examination. This can make the full diagnosis less accurate and less precise.
Clinicians and surgeons manually examine the injured knee joint for altered or increased joint play. However, due to the variability in size of the patient, size and experience of the surgeon, and the potential degree or subtlety of an injury, consistent and reproducible reports of joint play between surgeons is not possible. Many reports have documented that, whether diagnosis is performed manually or even with manual arthrometers, the manual application of torque to the knee joint varies widely between clinicians. This results in inconsistencies in the examination of joint play and, ultimately, the diagnoses made by clinicians.
Others have attempted to reduce the manual nature of such joint tests and to instrument the knee joint during testing. The objective has been to mechanically or objectively quantify or measure a change in the structure of the knee after ligament damage. Several devices have been developed in attempting to more accurately quantify the extent of injury or relative displacement and compliance of a ligament in the knee. In one example, such devices have been developed by Medmetric Corp. These devices include the KT-1000 and KT-2000 models. The KT devices are intended to measure the anterior-posterior translation of the tibia with respect to the femur. These KT devices attach to the patient's tibia during testing.
These KT devices attempt to quantify the findings achieved by a clinician performing the Lachman test and the Anterior Drawer Test. Force is applied to a handle on the device, which measures the force and delivers the amount of applied force to the clinician using sounds, such as a low pitched sound for a 15 pound force and a higher pitched sound for a 20 pound force. The applied force in the KT devices pulls anteriorly along the y-axis through a strap that wraps underneath the patient's calf. The translation is determined using a technique that measures the relative motion between a pad placed against the anterior tibia and a pad placed against the patella. The KT devices do not measure relative displacement or compliance in any of the other degrees of freedom in the knee. Also, quantified results from using the KT-1000 or KT-2000 devices have been found to have no correlation with patient satisfaction. In contrast, the subjective Pivot Shift test has been shown to be correlated with patient satisfaction.
Other devices are also known and include the Stryker KLT, the Rolimeter, the Rotameter, and the KSS system. These known devices use similar mechanisms to attempt to quantify the normal amount of joint play or motion between the femur and tibia in the knee joint, as well as any increased joint play or motion in the joint associated with ligament lengthening and damage. The applicant of the instant application has developed robotic knee testing (RKT) apparatuses, the basics of which are disclosed and described in U.S. publication nos. 2012/0046540 and 2014/0081181. The apparatus utilizes motors to perform knee movements during testing and sensors to measure degree of relative movement of the structures in the knee joint. Portions of the knee and leg can be stabilized or moved, as needed during testing.
Past methods of knee laxity testing in the past, both manual and instrumented, have a well-documented history of inaccuracy and inconsistency, both when testing the same patient from day to day and when two different examiners test the same patient. This is in part due to 1) the subjective nature, among examiners and among patients, of these prior examination and diagnosis techniques, 2) the complexity of the anatomy of the knee, 3) the lack of a system or method that is reliably repeatable to measure knee laxity, and 4) the accumulation of error that is introduced at different stages of an examination or diagnosis that is inherent in these prior known instruments and procedures. Multiple studies have brought into question the reproducibility and reliability of both the aforementioned manual knee exam techniques and the above-noted existing devices designed to simulate knee examinations. Many of these issues can be attributed to an inconsistent set-up of the exam or device, each of which can lead to inconsistent initial conditions at the start of the test and inaccuracies throughout the testing.
Introducing significant error at any one or more steps during a test can greatly affect, and invariably reduce, the accuracy of the ultimate diagnosis. The degree of error may often overwhelm the ability to obtain an accurate diagnosis. This is because, at every step of the testing and evaluation process, relatively small motions or movements are being detected, measured, and evaluated. Instrumented devices were developed as attempts to make measuring knee laxity or joint play more consistent and to try and reduce the degree of error involved, both in patient set-up and in testing the patient. However, these devices still typically rely on the examiner to determine the zero point or neutral position of the knee and/or require the examiner to manually apply the forces to the knee during testing and evaluation. These issues with existing instrumented devices lead to substantial inconsistency in the results.
Prior solutions have struggled to define a zero point or neutral position in the joint for each type of movement. Also, for rotation, prior solutions poorly distinguish between internal and external rotation. As a result, internal and external rotation have been typically combined into one single measurement. Further, when measuring AP translation, the KT-1000 relies on the tester to pull the tibia into anterior translation manually using a beeper to denote different force levels. The KT-1000 has a plastic mount that is designed to set the knee in the optimal testing position, but the manual aspect of the device provides for an inherent amount of error in the test.